1. Field of Invention
The present invention is directed to cables employing non-burnable and/or non-smokeable materials, particularly to plenum-rated twisted pair cables using such materials for insulation and jacketing.
2. Discussion of Related Art
Buildings such as office buildings, apartments and other facilities designed for temperature regulation, often include an air space or plenum between the ceiling and floor of successive floors of the building. The plenum is often contiguous throughout the floor and permits warm or cool air to be circulated throughout the building to regulate temperature. Because plenums offer accessibility to the various parts of a building and due to the general convenience of air conduits that typically extend throughout a facility, cabling structures, for instance, the structured cabling of an office local area network (LAN), are often wired through the plenum.
Should a fire occur in, for example, an office building, the walls, insulation and other fire retardant material are often capable of containing the fire within some portion of the building. However, fires that reach the plenum tend to draft and spread to other parts of the building quickly, particularly when the plenum is employed for other purposes and contains flammable material. Unless the communication cables employed in the plenum are flame and/or smoke retardant, a fire that has breached the plenum may ignite the cabling structures which may spread smoke and fire throughout a building. This may quickly intensify and increase the severity of a fire, making it more likely that burn and/or asphyxiation injuries to the occupants of the building will result and increasing the damage that may be done to the building.
Accordingly, various fire codes and in particular the National Electric Code (NEC) prohibits the use of cables in the plenum unless they have been first tested and exhibit satisfactory smoke and fire retardation. The various requirements set forth by the NEC, often referred to generally as the plenum rating, may be satisfied in a series of burn tests provided by, for example, the Underwriters Laboratory (UL).
Plenum rated cables are often made from various fluoropolymer materials. For example, insulating layers formed around the individual wires of a cable are often made from a fluoroethylenepropylene (FEP) material and jackets formed about the cable may be made up of an ethylene tetra fluoroethylene copolymer (ETFE) compound. Other fluoropolymers such as polytetrafluoroethylene (PTFE) may be employed in plenum rated cables as well. Such fluoropolymers are known to generally exhibit smoke and fire retardation characteristics sufficient to pass the burn tests, for example, the “peak smoke” and “average smoke” requirements.
However, fluoropolymer materials are relatively expensive and increase the production costs of manufacturing plenum rated cables. In addition, although fluoropolymers may be generally flame and smoke retardant, under intense flame and/or heat conditions, fluoropolymers may burn and produce smoke.